Traditional memories include a number of mode registers that may be programmed through a mode register set command and typically define various controls and settings for the memory device. The number and function of the various mode registers are typically defined by a standard, such as the double data rate 4 (DDR4) standard. Mode registers are typically configured to store a limited number of bits (e.g., 14 bits) that, when read by the memory device, convey control and setting information for performing memory operations.
Access to mode registers in these devices is typically a write only operation where the source of information stored in the mode register comes from the address bus instead of the device data pins, which require an extensive tuning/calibration process involving the same mode registers to function effectively. Many such devices, such as those compliant with the DDR4 standard, include a way to indirectly read back a subset of the contents of some predefined mode registers using the Multipurpose Register function (which is itself enabled/disabled by Mode Register Settings). However, previous standards had no method to read back the data stored in the Mode Registers.